Renewable and Sustainable Energy Reviews 41 (2015) 1190–1204

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Renewable and Sustainable Energy Reviews

journal homepage: www.elsevier.com/locate/rser

A review of Safety, Health and Environmental (SHE) issues of system

M.M. Aman a,n, K.H. Solangi b, M.S. Hossain c, A. Badarudin b, G.B. Jasmon a, H. Mokhlis a, A.H.A. Bakar c, S.N Kazi b a Department of Electrical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia b Department of Mechanical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia c UM Power Energy Dedicated Advanced Centre (UMPEDAC) Level 4, Wisma R&D, University of Malaya, Jalan Pantai Baharu, 59990, Kuala Lumpur, Malaysia article info abstract

Article history: Solar energy is one of the cleanest forms of energy sources and considered as a green source of energy. Received 4 April 2014 Solar energy benefit ranges from low carbon emission, no fossil fuel requirement, long term solar Received in revised form resources, less payback time and other. However like other power generation sources, solar energy has 11 August 2014 also some Safety, Health and Environmental (SHE) concerns. This paper presents the overview of solar Accepted 31 August 2014 energy technologies and addresses the SHE impact of solar energy technologies to the sustainability of human activities. This paper will also recommend the possible ways to reduce the effect of potential Keywords: hazards of widespread use of solar energy technologies. Solar energy technology & 2014 Elsevier Ltd. All rights reserved. Photo voltaic Life Cycle Assessment

Contents

1. Introduction...... 1191 2. Solar technology ...... 1192 2.1. Photovoltaic (PV) ...... 1192 2.2. Concentrating (CSP) ...... 1193 3. Life Cycle Assessment for harmonization in technology comparison ...... 1194 3.1. Carbon footprints...... 1194 3.2. Energy payback ratio (EPR) ...... 1194 3.3. Energy payback time (EPT) ...... 1195 3.4. Life-cycle and land-use (LCLU) ...... 1195 3.5. Levelized cost of electricity (LCOE) ...... 1196 4. SolarenergyimpactsonSafety,HealthandEnvironment(SHE)...... 1196 4.1. Positive impacts of solar energy ...... 1197 4.1.1. Saving in natural energy resources ...... 1197 4.1.2. Water consumption reduction ...... 1197 4.1.3. Land transformation/land use ...... 1198 4.1.4. Reduction of carbon dioxide emission ...... 1198 4.1.5. Noise and visual impacts...... 1199 4.2. Negative impacts of solar energy ...... 1199 4.2.1. Cost of land ...... 1200 4.2.2. Toxic chemical content in manufacturing ...... 1200 4.2.3. Ecological impacts ...... 1200 4.2.4. Decommissioning and recycling of solar panels...... 1201 5. Recommendations for a clean solar industry ...... 1201 6. Conclusion...... 1201

n Corresponding author. E-mail address: [email protected] (M.M. Aman). http://dx.doi.org/10.1016/j.rser.2014.08.086 1364-0321/& 2014 Elsevier Ltd. All rights reserved. M.M. Aman et al. / Renewable and Sustainable Energy Reviews 41 (2015) 1190–1204 1191

Acknowledgment ...... 1201 AppendixA...... 1201 References...... 1202

1. Introduction around 1700 TW and solar has a potential of 6500 TW. However, currently 0.02 TW of wind and 0.008 TW of solar is being utilized Due to current economic reforms and enormous technological [2]. Global environmental concerns and the escalating demand for developments around the world, the energy consumption is energy have also accelerated worldwide attention on green increasing exponentially. In 2011–2012, the energy consumption energy. Solar energy potential is largest among the natural energy was increased by 2.1% and in between 2000 and 2012, the energy resources. Solar energy is obtained from the thermal radiation consumption increase rate was 2.4% [1]. Total world energy use is emitted by the sun. At ground level, is attenuated also expected to rise by 56% in between 2010 and 2040 from 524 by the atmosphere to about 1000 W/m2 in clear sky conditions quadrillion British thermal units (Btu) in 2010 to 820 quadrillion within a few hours of noon – a condition called ‘full sun’. Solar Btu in 2040 [2]. Presently the maximum power consumption energy's potential estimates in the range from 1575 to 49,837 around the world at any given moment is 12.5 TW and it is EJ/year, which is roughly 3–100 times the world's primary energy expected by 2030, the world will require 16.9 TW [3]. According consumption in 2008 [9,10]. Nowadays, about 46 countries are to the International Energy Agency (IEA) statistics, 32.8% of actively promoting solar energy systems. The worldwide solar generation is based on oil, 27.2% based on coal, 20.9% is based on photovoltaic (PV) generation capacity continues to increase and natural gas and the remaining 19.1% based on nuclear, hydro and has become a rapidly growing industry [11]. IEA has estimated the others [4,5]. To fulfill the current projection of 16.9 TW by 2030, future growth of other renewable energy potential as shown in 13,000 large new coal power plants will be needed [2,6]. Heavily Fig. 1. By 2030 it is expected, that the renewable energy will reliance on fossil fuel will also increase the CO2 emission and the contribute 450 billion kWh/year. However solar contribution will largest emission is coming from the electricity sector. In US, be less in comparison to wind and bio-mass due to low efficiency electricity generators consumed 36% of country energy from fossil and other Safety, Health and Environmental issues. IEA has fuels and emitted 41% of the CO2 from fossil fuel combustion in estimated that by 2050, electricity generation from PV will reach 2011. Heavy rely on coal for electricity combustion is also among 4572 TWh (11% of global electricity production) and thus 2.3 Gt of the reason for such high CO2 emission. In 2011, 42% of electricity is CO2 emissions per year will be achieved [12–14]. Here it is also a produced from coal in US and accounted for 95% of coal consumed need to mention that the capacity factor of solar and wind based for energy [7]. power plant is smallest among all renewable and non-renewable The current need is to shift from conventional fossil fuel plants sources. Capacity factor is a measure of how often an electric to mix clean source of energy. The promotion of alternative generator runs for a specific period of time. The capacity factor of environmental friendly fuels can play a vital role to mitigate the solar PV based plant is 0.16, CSP based plant is 0.43 and wind has

CO2 emission and favor economic growth. However to cut down only a capacity factor of 0.40 [15]. Thus the efficiency of such the world CO2 emissions from 42 Gt to 39 Gt, the worldwide power plants needs to maximize to get the maximum output. investment in renewable energy sector assets need to be raised Solar energy benefit ranges from low carbon emission, no fossil from $100 billion to $500 billion during 2010–2030 [8]. Thus, in fuel requirement, long term solar resources, less payback time and addition to heavy investment in clean energy services, the power other. However like other power generation sources, solar energy consumption should also be decreased by introducing energy has also some Safety, Health and Environmental (SHE) concerns, efficient devices in the market to sustain the mixed clean energy which needs to be addressed. For example in PV solar cells source. manufacturing, some highly toxic materials like cadmium, lead, Renewable energy and nuclear power are the world's fastest- nickel and other compounds are used, which have been restricted growing energy sources; each of them is increasing by 2.5% per by the global environmental protection agencies [10,16–21]. Use of year [4,5]. Study has shown that, the wind has a total potential of such materials on mass scale is highly unhealthy for the local

Fig. 1. Projected non-hydropower renewable electricity generation, 2010–2035 [12]. 1192 M.M. Aman et al. / Renewable and Sustainable Energy Reviews 41 (2015) 1190–1204 habitat. In addition, like other sources of power generation, PV into wafers roughly 0.2 mm thick before the wafers are chemically modules also generate CO2 and other GHG at some stages in their treated and electrical contacts are made. They are cut from single life. Pure silicon metal (Simet) is used in PV panel manufacturing. crystals to become highly efficient. These modules convert up to Simet is produced in electric arc furnaces from quartz reacting at 15% of the energy from the sun into electricity, and test models very high temperatures with reduction elements like coal, coke, over 20% [34]. Polycrystalline (also known as multi-crystalline) charcoal, wood chips and the furnace graphite electrodes. The modules are made from cells containing lots of small silicon basic carbo-thermic reduction reaction for production of Simet is crystals [35]. This makes them the production cost cheaper but stated in Eq. (1). also slightly less efficient than mono-crystalline modules. Many small crystals provide polycrystalline modules a frosted look. SiO2 þ2C-Simet þ2CO ð1Þ While the 0.2 mm wafers in crystalline cells are already incre- The products of the process are silicon alloy, condensed silica dibly thin, the layers making the thin-film modules are of just fumes and recoverable heat energy. Until the last finish product in 2 μm which is about 40 times thinner than a strand human hair manufacturing, number of chemicals are used and (a micron is one-millionth of a meter). The layers can be deposited different GHG emitted in different chemical processes are elabo- on glass forming a panel similar to the crystalline modules, but rated elsewhere [22–24]. Carbon emission is highest in solar PV many other materials can also be used and even flexible panels can cells in comparison to other solar energy approach. Solar plants be made. Although the efficiency of thin-film panels is only about scrap also needs careful handling in recycling process. Solar 10%, they use less material and are cheaper than crystalline garbage comes under the electronic-waste (e-waste), thus careful modules [33,36–38]. handling is necessary in recycling process. This paper highlights The efficiency and share of the basic PV technologies is given in the SHE issues related to the solar technology. Table 1 [11]. Solar cells based on silicon (Si) semiconductors account for nearly 90% of 2011 sales of photovoltaic (PV) products. In 2011, annual production of Si-based PV has reached more than 2. Solar technology 15 GW [39]. There are also other emerging technologies, including concentrating photo-voltaic (CPV) and organic solar cells [11,40]. In general, solar technology has two major categories, i.e. solar Generally stated, PV module has an overall efficiency of 10% with photo-voltaic (PV) modules and concentrating solar power (CSP). the manufacturing cost of $1 per electrical Watt [19,28]. However PV cells convert sunlight energy into electrical energy by absorb- there has been a wide variation in cost, based on the type of ing photons from the light and thus atoms move from the lower materials. orbit to higher orbit and finally leave the parent atoms. CSP uses Electricity production from solar photovoltaic (PV) has contin- reflective surfaces to focus sunlight into a beam to heat a working ued its remarkable growth trend in 2011, even in the midst of a fluid in a receiver. The steam produced from the heat is used to financial and economic crisis [41]. In the past decade 2000–2011, drive the turbine and subsequently the generator is run to produce the enormous growth of PV markets was observed around the power [5,25–28]. world and particularly in Europe. The average global PV module price has also been dropped from about 22 USD/W in 1980 to less 2.1. Photovoltaic (PV) than 4 USD/W in 2009, while for the larger grid connected applications the prices have dropped down to roughly 2 USD/W The basic building block of the PV devices is a semiconductor in 2009 [42]. R&D work is also being carried for further improve- element known as PV cell. It converts solar energy into direct ment in efficiency and reduction in manufacturing cost of PV current electricity. When number of cells are interconnected, PV modules. IEA has also made ‘2050 roadmap’ for improvement in module is formed. The PV modules are integrated with a number solar technology efficiency and reduction in cost. It is targeted to of additional components, for example inverters, batteries, elec- achieve up to 25% and 15% efficiency in crystalline and thin film trical components, and mounting systems to form a PV system. PV technology respectively [12]. However on the other hand, produc- systems can be linked together to provide power ranging from a tion of these panels consumes substantial amounts of energy and few Watts to 100 kW [11,29,30]. PV modules are classified on the produces waste water and hazardous by-products which are basis of PV cells semiconductor materials. PV cell materials may released to the air during the manufacturing process [43,44]. differ based on their crystallinity, band gap, absorption, and Recycling technologies for reusing silicon from the solar cells are manufacturing complexity. Each material has a unique strength still not commercially in place but it has been proven that making and characteristic that influence its suitability for the specific a solar panel from recycled components require 1/3 of the energy applications [31,32]. than that of producing panels from the scratch. The total composi- There are three general families of photovoltaic (PV) modules tion of various solar module is represented in Table 2 [45], in the market today. They are mono-, polycrystal- however by considering weight, the solar cell materials are only line silicon, and thin film [33]. The cells in a mono-crystalline 4% of the total weight [46]. The point of concern in the manu- module are made from a single silicon crystal. This crystal is cut facture of solar panels is that the silver used in the module is

Table 1 The efficiency and share of the basic PV technologies [12].

PV technologies PV cell materials Efficiencies (%) Share in global market (%)

Crystalline silicon technology Mono-crystalline silicon (sc-Si) 14–20 85–90 Poly or multi-crystalline silicon (mc-Si). 13–15

Amorphous silicon (a-Si) 6–910–15 MicromorphSilicon (μc-Si) Thin films (CdTe) 9–11 Copper-indium-diselenide (CIS) 10–12 Copper-indium-gallium-diselenide (CIGS). M.M. Aman et al. / Renewable and Sustainable Energy Reviews 41 (2015) 1190–1204 1193 leftover and is considered a dangerous waste. Production of these (1) Trough systems use large, U-shaped (parabolic) reflectors panels in high quantities could also lead to the depletion of silver (focusing mirrors) which have oil-filled pipes running along resources. Research and development initiatives are taking place their center, or focal point, as shown in Fig. 2(a). The mirrored to recover key materials such as silicon glass, ethylene vinyl reflectors are tilted toward the sun, and focused the sunlight acetate (EVA) foil and aluminum from existing panels which can on the pipes to heat the oil inside as much as 750 1F. The hot be recycled and used to make new panels [43,47]. Research and oil is then used to boil water, which makes steam to run development initiatives are taking place to recover key materials conventional steam turbines and generators [50,52,53]. such as silicon glass, EVA foil and aluminum from existing panels (2) Power tower systems also called central receivers, used in which can then be recycled and used to make new panels. many large, flat heliostats (mirrors) to track the sun and focus its rays onto a receiver. As shown in Fig. 2(b), the receiver sits 2.2. Concentrating solar power (CSP) on top of a tall tower in which concentrated sunlight heats a fluid, such as molten salt which can be as hot as 1050 1F. The CSP technologies produce electricity by concentrating the sun's hot fluid can be used immediately to make steam for elec- rays to heat a medium that is used either directly or indirectly to tricity generation or stored for later use [48,49]. heat a fluid in engine process (e.g., a steam turbine) which is used (3) Dish/engine systems use mirrored dishes (about 10 times to drive an electrical generator. In current commercial designs of larger than a backyard satellite dish) to focus and concentrate heat-collection element in CSP, a heat transfer oil is circulated sunlight onto a receiver as shown in Fig. 2(c). In dish/engine through the steel pipe where it is heated (to nearly 400 1C), but system, the receiver is mounted at the focal point of the dish. systems using other heat transfer materials such as circulating To capture the maximum amount of solar energy, the dish molten salt or direct steam are currently being used [10]. Molten assembly tracks the sun across the sky. The receiver is salt retains heat efficiently, so it can be stored for days before integrated into a high-efficiency ‘external’ combustion engine. being converted into electricity. That means electricity can be The receiver, engine, and generator composed a single, inte- produced during the periods of peak in the cloudy days or even grated assembly mounted at the focus of the mirrored dish several hours after sunset [48,49]. [48,54,55]. In general, CSP technology utilizes three alternative technolo- gical approaches to heat the medium: trough systems; power CSP has reached a cumulative installed capacity of about tower systems; and dish/engine systems as shown in Fig. 2 and 0.7 GW, with another 1.5 GW under construction. The capacity described below [50,51]. factors for a number of these CSP plants are expected to range from 25% to 75% and it can be higher than PV because CSP plants contain the opportunity to add thermal storage where there is a commensurate need to overbuild the collector field to charge the thermal storage [10]. Projects are now under development or Table 2 under construction in many countries including China, India, Composition of c-Si and thin film modules from PV cycle study-2007 [45]. Morocco, Spain and the United States and are expected to produce Proportion c-Si a-Si CIS (copper CdTe electricity a total of 15 GW [56]. US DoE has focused on developing in % (crystalline (amorphous indium (cadmium the CSP technologies to achieve the technical and economic silicon cells) silicon cells) diselenide cells) telluride cells) targets. The SunShot Initiative program of US DoE goal is to reduce the levelized cost of electricity generated by CSP to $0.06/kWh or Glass 74 90 85 95 Aluminium 10 10 12 o0.01 less, without any subsidy, by the year 2020. The DOE SunShot Silicon Approx. 3 0.1 –– Initiative is a national collaborative effort to make solar energy Polymers Approx.6.5 10 6 3.5 cost-competitive with other forms of electricity by the end of the Zinc 0.12 o0.1 0.12 0.01 decade [52,57]. CSP has several advantages over other technolo- Lead o0.1 o0.1 o0.1 o0.01 gies, like one advantage of CSP plants is that they are often located Copper 0.6 – 0.85 1.0 (cables) in areas with limited amenity or esthetic value. Desert land for Indium –– 0.02 – solar plants could be in many ways better than agricultural land Selenium –– 0.03 – for biomass energy [58]. Greenhouse gas emissions for CSP plants Tellurium –– – 0.07 – –– – are estimated to be in the range of 15 20 g of CO2-equivalent/kWh, Cadmium 0.07 fi Silver –– – o0.01 which is much lower than CO2 emissions from fossil- red plants which are 400–1000 g CO2-eq/kWh [58].

Fig. 2. Schematic diagram of different arrangement of CPS panels [52]. 1194 M.M. Aman et al. / Renewable and Sustainable Energy Reviews 41 (2015) 1190–1204

3. Life Cycle Assessment for harmonization in technology with CCS which will have carbon foot prints ranging from 160 to comparison 280 gCO2eq/kWh [31,64]. In case of renewable energy sources, such plants do not generate GHG during operation, most of the emissions Life Cycle Assessment (LCA) is a tool for sustainability analysis come during the construction phaseandtheproductionoffuels of renewable and conventional energy technologies [21]. LCA aims (where applicable). For generators based on ambient energy flows, at evaluating all environmental impacts associated with a given such as solar energy, the local energy resource also has an important product or service at all stages of its lifetime from ‘cradle to grave’ influence on the carbon footprint values. This is because higher such as from resource extraction and processing, through con- electricity outputs cause lower footprints, as total emissions are struction, manufacturing and retail, distribution and use, repair spread over a greater amount of electricity [31,64]. Similarly location and maintenance, disposal/decommissioning and reuse/recycling has also an important effect on the carbon footprint. For example in [59,60]. The goal of the LCA is to bring harmonization in technol- case of wind generation, figures from one UK study indicate that a ogy to reduce the uncertainty for environmental impacts of micro-wind turbine would have a carbon footprint of around renewable and make the information useful to decision-makers 38 gCO2eq/kWh for locations with an average annual wind speed in the near term [61]. The Intergovernmental Panel on Climate of4.5m/s.Thisistheminimumwindspeedrecommendedforsmall Change (IPCC) special report on renewable energy sources and wind systems by the industry trade body. The same study indicates climate change mitigation provides a comprehensive review con- that locations with an average wind speeds of 6 m/s would give cerning these sources and technologies, the relevant costs and footprints of 20 gCO2eq/kWh, while locations having 3 m/s wind benefits, and their potential role in a portfolio of mitigation speed would give 96 gCO2eq/kWh [31,64]. In general fossil fueled options [5,62]. Four terminologies are commonly used in compar- electricity generation has the largest carbon footprint (above ing different technologies (for example, among solar technologies) 1000 gCO2eq/kWh) and renewable technologies have low carbon and power generation sources (conventional and renewable). footprints (o100 gCO2eq/kWh). Future carbon footprints can be reduced for all electricity generation technologies if the high CO2 (1) Carbon footprints emission phases are fueled by low carbon energy sources [64]. (2) Energy pay back ratio (EPR) (3) Energy pay back time (EPT) (4) Life cycle land use (LCLU) 3.2. Energy payback ratio (EPR) (5) Levelized cost of electricity (LCOE) Energy payback ratio (EPR) is the ratio of total energy produced during a system's normal lifespan, divided by the energy required 3.1. Carbon footprints to build, maintain and fuel it. If a system has a low payback ratio, it means that much energy is required to maintain it and this energy

Carbon footprint is used to find the amount of CO2 that enters to is likely to produce many environmental impacts. A high ratio theatmosphereoverthefulllifecycle(fromcradletograve)ofa indicates good environmental performance. If a system has a process or product. It is expressed as grams of CO2 equivalent per payback ratio between 1 and 1.5, it consumes nearly as much kilowatt hour of generation (gCO2eq/kWh) [63].Carbonfootprints energy as it generates, so it should never be developed. For fossil are sensitive to various factors including operating conditions and fuels, it means environmental impacts at extraction, transporta- country of its manufacture. Renewable energy sources also have a tion and processing of fuels. For renewable sources, it means carbon footprint value because they also emit greenhouse gases environmental impacts at building the facility [66]. If the ratio is particularly during construction phase. Fig. 3 shows comparison of close to unity, it means it consumes as much energy as it produces, the carbon foot prints values for conventional and renewable energy so it should never be developed. Thus the value of EPR should be based power plants. The carbon emission from fossil fuel based as large as possible to generate favorable economics. However the conventionalpowerplantsissignificantly high as comparison with amount of pollutants emitted per kWh of electricity generation and renewable energy based power plants. In case of fossil fuels, should be as low as possible [67–69]. The EPR for conventional and carbon capture and storage (CCS) technologies have the potential to renewable energy resources is shown in Fig. 4. reduce emissions from fuel combustion considerably, but are yet to Fig. 4 shows that renewable energies have large variations, due be proven feasible at full scale. Modeling shows coal-fired generators to variable site-specific conditions. Hydropower clearly has the

Fig. 3. Summary of life-cycle GHG emissions for selected power plants [65]. M.M. Aman et al. / Renewable and Sustainable Energy Reviews 41 (2015) 1190–1204 1195

Fig. 4. Energy payback ratio (EPR) for conventional and renewable energy resources [10]. highest performance, with EPR of 205 and 267 compared to fossil Table 3 fuel systems with typical ratios of 5–7. Wind power also has a very Energy payback time of electricity generating technologies [10]. good performance (ratio of 80). However, this ratio is overesti- Technology Energy payback time (EPT) Most commonly mated because the calculations did not consider the need for stated life (years) fl backup capacity to compensate for wind uctuations [66]. Low value High value

3.3. Energy payback time (EPT) Brown coal new subcritical 1.9 3.7 30 Black coal new subcritical 0.5 3.6 30 Black coal new subcritical 1.0 2.6 30 Energy payback time (EPT) is the time required for a generation Natural gas (open cycle) 1.9 3.9 30 technology to generate the amount of energy that was required to Natural gas (combined cycle) 1.2 3.6 30 build, fuel, maintain and decommission it. The EPT is closely linked Heavy water reactors 2.4 2.6 40 to the energy payback ratio and depends on assumptions made on Light water reactors 0.8 3.0 40 Photo-voltaic 0.2 8.0 25 the lifetime of a technology [59,70–73]. EPT also exists as a Concentrating solar 0.7 7.5 25 criterion for LCA analysis of different technologies. Table 3 lists Geo thermal 0.6 3.6 30 the EPT of different power system technologies [10]. Wind turbines 0.1 1.5 25 The main reasons for variation in EPT values in Table 3 are fuel Hydro electricity 0.1 3.5 70 characteristics (e.g. moisture content), cooling method, ambient and cooling water; temperatures and load fluctuations (coal and gas), uranium ore grades and enrichment technology (nuclear), crystal- line or materials (PV solar cells), economies of 3.4. Life-cycle and land-use (LCLU) scale in terms of power rating (wind) and storage capacity and design (concentrating solar). For some renewable energy sources, Different critics consider different criteria for finding out the for example wind and PV, energy payback times have decreased land usage in Life Cycle Assessment. Many critics consider that because of economies of scale and technological progress [59]. renewable energy resources occupy more land as compared to However, the location‐specificcapacityfactorhasamajorinfluence conventional resources [76–78]. However, some authors did not on the energy payback time in particular for intermittent renewable include the land transformation (land use change) and land energy sources. In the case of fossil fuel and nuclear power occupation (land use for a certain period) while comparing technologies, the impact of fuel extraction and procession may technologies [79]. The land transformation indicates the area of increase in parallel with the decline in conventional fuel and rise in land altered from a reference state (unit: m2), while the land unconventional fuel. Fig. 5 shows the EPT for silicon and CdTe PV transformation occupation denotes the area of land occupied and modules [74]. The payback period for thin films based solar cell is the duration of the occupation (unit: m2 year). Fig. 6 represents less than the wafer based Si. For example, EPBT for CdTe material the total land-area transformation for different electricity genera- plants is 1.1 years compared to 1.7, 2.2, and 2.7 years for ribbon, tion sources [80–83]. Table 4 shows the overall land use for multi-, and mono-Si technology respectively [75]. renewable energy plant to supply electricity. 1196 M.M. Aman et al. / Renewable and Sustainable Energy Reviews 41 (2015) 1190–1204

3 Module 2.5 Frame 2 BOS 1.5 Years 1 0.5 0 production CdTe, 9% US production Slurry recycling Slurry recycling Slurry Multi-Si, 13.2% Multi-Si, 13.2% Multi-Si, Multi-Si, 14.0% Multi-Si, Mono-Si, 14.0% 14.0% Mono-Si, Ribbon-Si, 11.5% Ribbon-Si, CdTe, 8% European CdTe, European production European production production European European production European production

Fig. 5. Energy payback time for silicon and CdTe PV modules [74].

From Fig. 6, it could be observed that the PV transforms the least amount of land in comparison with other renewable tech- nologies. Also LCA is highly sensitive to the location and environ- mental condition of the exposed side [80,85]. The land occupation per unit of electricity generation from conventional power sources like coal and nuclear sources is very sensitive to the length of ’ recovery for allocated area. Fig. 7 represents the land occupation Fig. 6. Life-cycle land transformation for fuel cycles based on 30-years timeframe [80]. patterns for conventional and renewable energy systems for 1 GWh of electricity [23,72,78–80]. Fig. 7 shows that the biomass Table 4 farming entails the greatest land occupation (380,000 m2 year/GWh) Estimation of the land for renewable energy plant to supply electricity [84]. followed by nuclear-fuel disposal (300,000 m2 year/GWh). However Technology Land per year (km2/GW) the PV power plant with 13% efficiency requires 9900 m2 year/GWh of land occupation [80]. Flat-plate PV 10–50 Solar thermal or PV concentrator 20–50 Wind 100 3.5. Levelized cost of electricity (LCOE) Biomass 1000

LCOE represents the per-kilo-watt-hour cost (in real dollars) of building and operating a generating plant over an assumed financial life and duty cycle. Capital costs, fuel costs, fixed and variable operations and maintenance (O&M) costs, financing costs, and an assumed capacity factor for each plant type are included in calculating LCOE [86]. It is calculated using Eq. (2) [87]. Total life cycle cost LCOE ¼ ð2Þ Total lifetime energy production It is often stated as a convenient measure of the overall competiveness of different generating technologies. Fig. 8 repre- sents the LCOE for conventional and renewable energy sources. In Fig. 8, the LCOE for each technology is evaluated based on the capacity factor indicated in Table 5 [88], which generally corresponds to the high end of its likely utilization range. The duty cycle for intermittent renewable resources, wind and solar, is not operator controlled, but dependent on the weather. The capacity factor ranges for these technologies are as follows: wind – 31–45%, wind offshore – 33–42%, solar PV – 22–32%, solar thermal – 11–26%, and hydroelectric – 30–65%. The levelized costs are also affected by regional variations in construction labor rates Fig. 7. Land occupation for 1 GWh of electricity from conventional and renewable and capital costs as well as resource availability [86]. energy [80]. In summary, PV technologies are proved to be sustainable and environmental-friendly regarding the GHG emission rate, EPBR, shortened PV system energy pay-back times. The latter is expected EPBT and land usage in comparison to conventional energy sources. to be reduced from maximum two years in 2010 to 0.75 year in The levelized cost of solar power generation is found higher than 2030 and below 0.5 year in the future. Finally, the operational the existing possible methods. Table 6 summarizes a set of general lifetime is expected to increase from 25 to 40 years. technology targets for PV systems up to 2050, expressed in terms of (maximum) conversion efficiency, energy-payback time, and opera- tional lifetime [89]. Typical commercial flat-plate module efficien- 4. Solar energy impacts on Safety, Health and Environment (SHE) cies are expected to increase from 16% in 2010 to 25% in 2030 with the potential of enhancement up to 40% in 2050. Concurrently, the Solar energy is considered as one of the cleanest forms of power use of energy and materials in the manufacturing process will generation. However as compared to other energy resources, solar become significantly more efficient; leading to the considerably energy has also some disadvantages. Solar energy benefits could be M.M. Aman et al. / Renewable and Sustainable Energy Reviews 41 (2015) 1190–1204 1197 enlisted as, low carbon emission, no fossil fuel requirement, long solar market, needs proper planning to handle the future solar term solar resources, less payback time and others. However it has garbage. Otherwise it will become difficult to handle tons of wastes. been seen that every form of generation source has carbon emission For example, a 10 MW electricity generation plant consumes at some stages. In the manufacturing of PV solar cells, some highly 2000 tons of thin-film solar panels needed [91]. These issues are toxic materials like cadmium, lead, arsenic, nickel and others are discussed in detail in subsequent sections. used, those have been restricted by global environmental policies fi [10,17]. For example in thin- lm cadmium-telluride (CdTe) PV 4.1. Positive impacts of solar energy modules, restricted e-product cadmium is used which is also known as human carcinogen [12,90]. Such material use on mass scale is Solar energy is one of the cleanest forms of energy, with highly harmful from the SHE point of view. Solar plants scrap also remarkable solar potential available all over the world. Benefits needs careful handling in recycling process. Solar garbage comes of solar energy lies with the minimization of utilization of natural under the e-waste. Consistent annual growth and high production in resources particularly those diminishing very fast (like oil, coal and

others), reduction in emission of CO2 and consumption of water and the availability of huge amount of Si semiconductor materials availability for solar panel constructions. These advantages are discussed in detail in this paper.

4.1.1. Saving in natural energy resources The fossil fuel resources are depleting very fast, depending on the increase of energy consumption. The energy consumption and production rate is increasing and it is expected by 2025, energy consumption will supersede the energy production rate, thus the world has to face the energy shortage problem. The yearly statistics of energy production and consumption is given in Table 7 [92]. According to [92] statistics report, the daily world energy fuel consumption has increased, up to 3.1% in oil, 7.4% in gas and 7.6% in coal consumption per day basis from 2009 to 2010. The world proven energy reserves are expected to be expired in 100 years. Fig. 8. Levelized cost of energy (LCOE) for conventional and renewable energy The expected end of energy reservoirs is given by reserves to sources [88]. production ratio (R/P ratio), which is measured in years. R/P ratio depends on current energy reservoirs and the production/con- Table 5 sumption during that year. The proved reserves of fossil fuel is Capacity factors of conventional and renewable energy sources [88]. given in detail in Table 8. If the reserves remaining at the end of Technology Capacity Technology Capacity the year are divided by the production in that year, the result is the factor factor length of time that those remaining reserves would last if production were to continue at that rate. Renewable energy is Wind, onshore 0.38 Hydropower 0.50 Wind, offshore 0.39 Bio-power 0.83 although vast in quantity but still the need for fossil fuels could Solar, photovoltaic 0.16 Fuel cell 0.95 not be diminished. Fossil fuels are considered reliable source of Solar, concentrating solar 0.43 Natural gas combined 0.87 energy, however tidal, wind and solar are intermittent sources of power (CSP) cycle energy and depend on environmental conditions. Geologists also Coal, integrated gasification 0.85 Natural gas combustion 0.30 advise us that, it is necessary to leave enormous amount of fossil combined cycle turbine Enhanced geothermal system 0.95 Pulverized coal 0.85 fuels in the ground to reduce the risk of climatic change [93]. (EGS) Nuclear 0.90 Geothermal, 0.95 hydrothermal 4.1.2. Water consumption reduction Earth is considered as a blue planet, 70% water and rest of the 30% is land. Although out of 70%, fresh water available is only 3%

Table 6 [94]. According to the World Health Organization report, one-third PV technology target [89]. of the Earth's population is leaking the necessary quantities of water from their requirement. On the other hand United nation Target year 2008 2020 2030 2050 estimates that by 2050, half of the world's population will live in those countries which will have shortage of water, largely in Asia, Typical flat-plate module Up to 16% Up to 23% Up to 25% Up to 40% – efficiencies Africa, and Latin America [95 97]. The expected water require- Typical maximum system 2 years 1 year 0.75 year 0.5 year ment till 2050 is given in Table 9. energy pay-back time One of the largest consumption is due to conventional power (in years) in 1500 kWh/kWp plants for the condensing portion of the thermodynamic cycle. regime Operational lifetime 25 years 30 years 35 years 40 years Average water consumption (gal/MWh) for conventional and rene- wable power plants is shown in Fig. 9 [98]. Water consumption is

Table 7 Energy production and consumption (in million tonnes oil equivalent) [92].

Years 2000 2005 2010 2015 2020 2025 2030

Total energy production 9387.00 10,867.20 12,145.60 13,565.80 14,685.11 15,619.62 16,604.65 Total energy consumption 9382.42 10,800.94 12,002.35 13,360.41 14,627.05 15,634.60 16,631.56 1198 M.M. Aman et al. / Renewable and Sustainable Energy Reviews 41 (2015) 1190–1204

Table 8 Proved reserves of fossil fuels (BP statistical review-2011) [60].

Region Oil Natural gas Coal

Thousand Share of Trillion Share of Total Share of million total (%) cubic total (%) million total (%) barrels metres tonnes

North 74.3 5.4 9.9 5.3 245,088 28.5 America South and 239.4 17.3 7.4 4.0 12,508 1.5 Central America Europe and 139.7 10.1 63.1 33.7 304,604 35.4 Eurasia Middle East 752.5 54.4 75.8 40.5 32,895 3.8 Africa 132.1 9.5 14.7 7.9 Asia Pacific 45.2 3.3 16.2 8.7 265,843 30.9 World 1383.2 100.0 187.1 100.0 860,938 100.0 R/P* 46.16 58.60 118.37

n Reserves-to-production (R/P) ratio.

Table 9 Water requirements for energy production in the world [94,95].

Year 2005 2015 2035 2050

Total world water for energy 1815.6 1986.4 2087.8 2020.1 (billions m³) Fig. 9. Estimated life cycle water consumption factors for conventional and renewable generation technologies [98]. Note: EGS¼enhanced geothermal system; CT¼combustion turbine; CC¼combined cycle; IGCC¼integrated gasification com- bined cycle; and PC¼pulverized coal, sub-critical. vital and is a great concern especially for countries like Singapore and Saudi Arabia, where clean water is highly valuable. Dubai, high- tech city, has been built in a desert and has the world's highest per Table 10 capita rate of water consumption [99].FromFig. 9, it can be seen Land-use requirements for PV and CSP projects in the United States [103]. that using renewable energy sources, water can be preserved and could be effectively utilized for other purposes. In case of PV, water Technology Direct area Total land use (acres/MWac) (acres/MWac) use for operations is minimal. Experimental evidence demonstrates that although frequent washing increases output, it likely leads to Small PV (41MW,o20 MW) 5.9 8.3 economic losses [100]. Concentrating solar thermal plants (CSP), Large PV (420 MW) 7.2 7.9 like all thermal electric plants, require water for cooling. Water use CSP 7.7 10 depends on the plant design, plant location, and the type of cooling system. The water usage for CSP could be significantly reduced by using dry cooling approaches. However, the tradeoffs to these water savings are higher costs and lower efficiencies. In addition, dry- no specific land is required for extraction [93,104]. Table 10 shows cooling technology is significantly less effective at temperatures the summary of land-use requirements for PV and CSP projects in above 100 1F [10,101]. the United States [103]. Direct land use represents the disturbed land due to physical infrastructure or development due to solar and total area use represents all land enclosed by the site boundary. 4.1.3. Land transformation/land use Solar like other renewable energy resources has some distinct features as compared to conventional source of energy. Like con- 4.1.4. Reduction of carbon dioxide emission ventional power plants, solar energy sources do not need further One of the main advantages of solar energy is zero air pollution extraction of resources once the infrastructure has been developed. during power generation. This makes the solar energy among the Moreover the land could be used for other purposes, like plantation cleanest form of energy on earth. Solar energy does not burn oil, and shading [102]. Direct land-use requirements for small and large thus it does not produce any toxic gases. However some toxic PV installations range from 2.2 to 12.2 acres/MW, with a capacity- materials are widely used in solar cells manufacturing. These weighted average of 6.9 acres/MW. Direct land-use intensity for CSP environmental tolls are negligible when compared with the installations ranges from 2.0 to 13.9 acres/MW, with a capacity- damage inflicted by conventional energy sources. The burning of weighted average of 7.7 acres/MW [103]. On the other hand fossil fossil fuels releases roughly 21.3 billion metric tons of carbon fuel based plants need lands for their power plant as well as for the dioxide into the atmosphere annually [105,106] stated that a extraction of resources. Land transformation (primarily for residen- 50 MW parabolic trough power plant can eliminate 80,000 tons tial or industrial areas) period for fossil fuel based plants is based on of CO2 emissions annually. Fig. 10 shows the carbon foot prints the amount of extraction per day. Also in case of fossil or nuclear values for renewable energy based power plants. plants land is marked and left, in search of fuels for future use. On Solar energy although has the largest carbon foot prints value the other hand, Si material exists in the nature in abundant quantity, in renewable technologies. However future improvements in M.M. Aman et al. / Renewable and Sustainable Energy Reviews 41 (2015) 1190–1204 1199 cumulative GHG emissions from PV are likely to arise from construction phase and especially for large schemes during the improvements in module efficiency, increased lifetime, less silicon operational phase. Solar panels contain no moving parts and thus mass per module and lower use of electricity for the production produce no noise. Wind turbines, by contrast, require noisy process [65]. It is also important to note that solar PV technology is gearboxes and blades. However fossil fuel based plants and a fast-improving technology and frequent LCA studies are being renewable source of energy (including wind and hydro) have published in order to keep the pace with the advancements. noise problems [21,60,107,108]. The noise problem from power plants makes it unsuitable for placement nearer to the population. Proper sites are marked for their placements. Solar technology is 4.1.5. Noise and visual impacts changing is very fast. Options for reduction of energy demand Solar modules do not suffer with the noise problem. Solar must always be considered along with the assessment of PV energy is a static source of power generation with no rotating application. Instead of roof-topped panels, special bricks with parts. Also, there will be some employment benefits during the integrated special PV modules are also made. Fig. 11 shows such type of construction giving esthetic look [60,109]. Visual intrusion is highly dependent on the type of the scheme and the surroundings of the PV systems. It is obvious that, if a PV system is applied near an area of natural beauty, the visual impact would be significantlyhigh.Incaseofmodulesintegratedintothefacadeof buildings, there may be positive esthetic impact on modern buildings in comparison to historic buildings or buildings with cultural value.

4.2. Negative impacts of solar energy

Solar energy is considered as a ‘Green Source’ of energy. However there are some Safety, Health and Environmental issues, which should be addressed before the wide spread application of solar technology. Solar panels are based on nanotechnology, which is considered as a ‘clean tech’ technology [114].Toseetheimpactof solar panel, its life could be split into three stages, manufacturing, operation (generation), decommissioning. It is true that photovoltaic Fig. 10. Carbon Footprints for renewable electricity [64]. solar panels do not pollute the air during power generation however

Fig. 11. Solar energy constructed outlook; (a) residential house based on building integrated photovoltaic/thermal technology [110]; (b) Integrated combined solar thermal and electric generation building [111] at John Molson School of Business, Concordia University. (c) The Solar Ark [112, 113], a sign board in Japan under Electric Co., Ltd. (d) Solar Brick LED Lights. 1200 M.M. Aman et al. / Renewable and Sustainable Energy Reviews 41 (2015) 1190–1204 manufacturing process of them involves many toxic materials, which tive (RoHS) [118–122]. However the European Union decision highly is highly harmful from SHE perspective. There are some concerns affected the production of solar panel based on cadmium telluride after the completion of expected life of panel and in their recycling (CdTe). In November 2010, EU law exempted the solar panel from a process. These issues will be discussed in this section [115]. ban in order to facilitate the solar manufacturing industry and also to attain the set targets for renewable energy generation [123].These toxic materials have special concerns, particularly for local habitats. In 4.2.1. Cost of land recent years, September 2011, accidents due to dumping of hazardous Large-scale solar farms need a big space for their installation. chemicals into the water supply has led to local protest and finally Approximately 1 m2 of land produces 200 W of electricity, resulted the shutdown of the company [124]. PV panels are threat to depending on the location, efficiency and other environmental the environmental contamination if improperly disposed of upon conditions [6,116,117]. This problem becomes prominent for those decommissioning due to the use of toxic materials in their composi- countries which have already high population density like Singa- tion [76]. On the other hand, the accidental release of heat transfer pore, having an area of 697 sq.km [66], with population density fluids (water and oil) from parabolic trough and central receiver above 7680/sq.km. Finding cheap land in such countries is quite systems could form a health hazard. The hazard could be substantial difficult. Also high cost of land will also affect the per unit in some central tower systems, which use liquid sodium or molten electricity cost. Land use could be minimized by increasing the saltsasaheat-transfermedium.Indeed a fatal accident has occurred solar panels efficiency or to mount the cells on a rooftop [6]. With in a system using liquid sodium. These dangers could be avoided by current efficiency of solar panel, the top roof area of houses in USA moving to volumetric systems that use air as a heat-transfer medium. will only fulfill the 1/10th of total US energy requirement [6]. Central tower systems have the potential to concentrate light to intensities that could damage eyesight. Under normal operating 4.2.2. Toxic chemical content in solar panel manufacturing conditions this should not pose any danger to operators, but failure Different chemicals are used in manufacturing of solar panels, of the tracking systems could result in straying beams that might pose particularly during extraction of solar cell. For example, cadmium (Cd) an occupational safety risk at site [60]. The partial list of toxic materials is used in cadmium telluride based thin film solar cells as a used in solar industry, their use and impact on human health, safety semiconductor material to convert solar energy into electrical energy andenvironmentsarepresentedinTable 11. which is highly toxic element. National Institute of Occupational Safety & Health (NIOSH) considers cadmium dust and vapors as carcinogens (causing cancer). Similarly many hazardous chemicals are used as 4.2.3. Ecological impacts solvents to clean dust and dirt from the solar panels. European Union Solar energy facilities have direct impacts on local habitats and has initially banned Cd, Pb, Hg and other toxic compounds as per nearby surroundings. The construction of solar farms on large the regulations of the Restriction of Hazardous Substances Direc- scale needs clearing of land which adversely affects the native

Table 11 Safety, Health and Environmental (SHE) impact from the toxic compounds [78,80,125–127].

Toxic Compounds Purpose Safety, health and environmental impact

Ammonia (NH3) To produce anti-reflective coatings for solar PV Skin irritation, eyes irritation, throat problem, lungs problems, mouth and modules. stomach burns. Arsenic (As) Used in GaAs solar PV cells, resulted from the Heart beat problems, throat infection, lung cancer, nausea, vomiting, reduced decomposition of GaAs blood cells, skin darkening, red spot on skin, liver problem, etching in hands and feet. Silicon (Si) Used as a PV semiconductor material Crystalline Si causes respiratory problems, irritating skin and eyes, lung and mucus problems Lead (Pb) To wire, solder photovoltaic electrical components. Damages nervous system, weakness in bones, can also cause anaemia,high level exposure resulting in miscarriage for pregnant woman, damages the brain and kidneys, highly carcinogen element.

Nitric acid (HNO3) To clean wafers and reactors, remove dopants. Potential cause for chemical burns. Sulfur hexafluoride (SF6) Used to etch semiconductors and clean reactors in The most powerful greenhouse gas known. PV manufacturing. Cadmium (Cd) Cd is used in cadmium telluride based solar cells as Cd dust and vapours are highly toxic and considered as carcinogens. Also a semiconductor to convert solar energy into effectthe respiratory system, kidneys and blood cells and can cause prostate, electricity. diarrhoea, chest tighten and lung cancer.

Hydrogen (H2) Used in manufacturing amorphous-Si solar cells. Highly explosive. Hexavalent Chromium (Cr-VI) Used in screw, solar chassis board and as a coating Cr is a carcinogenic element, means causes cancer. material in solar panel to absorb solar radiation. Polybrominated biphenyls (PBBs) Used in circuit boards and solar panel inverters Recognized as toxic and carcinogenic and are described as endocrine and brominated diphenylethers disrupters. (PBDEs) Acetone These solvents are used to clean microscopic dirt Eyes andnose irritation, throat infection, kidney and liverproblem, nerve and dust off of chips. damage, birth defects, sexual problems including lowered ability to reproduce males. Iso-propanol To clean microscopic dust and dirt from solar chips. Vomiting, Eyes irritation, depression, dermatitis, nausea, unconsciousness, respiratory failure, death or coma. Toulene Headaches, hearing loss, confusion, memory loss, pregnancy problems, retarded growth. Xylene Skin irritation, eye irritation, nose infection, throat and breathing problems, pregnancy problems, liver and kidneys infection. 1,1,1-Trichloroethane Dizziness and loss of mind, reduced blood pressure, unconsciousness, stop heart beating. Hydrochloric acid (HCl) To produce electrical grade silicon, clean and etch Skin problem, eyes and nose infection, respiratory problem, food digestion, semiconductors mouth and throat infection, respiratory depression. M.M. Aman et al. / Renewable and Sustainable Energy Reviews 41 (2015) 1190–1204 1201 vegetation, wildlife and loss of habitat. If at the optimum solar site, natural resources, their main advantage is total absence of almost any trees and bushes exists and blocking the sunrays, it needs to be air emissions or waste products during operation. The current growth removed [6]. The native drainage and irrigation system also of solar industry is remarkable however the above SHE issues should disturbed due to solar sites. The presence of cattle animals can not be neglected. Solution of one problem of lack of energy resour- reduce the efficiency of PV modules due to the increased rate of ces for power generation should not result in generation of other dust and dirt in the surroundings. Special chemicals are used for problems. People are very much concerned about the disposal and dust suppressants and herbicides cleaning at solar facilities, which hazardous wastes due to solar power plants waste [77]. Following results in contamination of the surrounding and groundwater recommendations could be adopted to make the solar industry a [57,128]. Engineering methods can be used to mitigate these clean or nearer to clean industry: impacts. On the other hand, CSP generates electricity by driving the heat engines located on the ground. The high temperature of Reduction and step-by-step elimination of hazardous materials fluids or materials is achieved by receiving the energy from optical used in chemical processing of semiconductor materials. concentrated solar receiver, as shown in Fig. 12. The height of CSP Life time for solar equipment should be improved, in order to and the reflected light beams cause interference with aircraft increase the energy pay back ratio and thus minimizing GHG operations [83,129]. and CO2 emission. Efficiency of solar panels should be improved in order to minimize the land use and thus generating minimum ecological impacts. 4.2.4. Decommissioning and recycling of solar panels Need to carry out a thorough survey to understand the environ- Solar modules present some SHE concerns after the completion mental impact of setting solar panels on local habitants. of their expected life (20–30 years). Disposing them on landfills is a Need to carry out research to find out eco-friendly semi- big challenge for local municipal committees due to the use of small conductor materials and other chemicals used for their amounts of hazardous materials. Authors in [91] have discussed treatment. centralized and decentralized recycling strategies. The current Strict guidelines should be followed during manufacturing of growth of solar market is quite large and the time is to do proper solar panels, for human safety. planning to handle the future solar garbage, otherwise it will become Strict guidelines should be followed during disposal of hazar- difficult to handle tons of wastes. For example, to produce 10 MW dous wastes, generated in solar panel manufacturing. electricity there is a need of 2000 t of thin-film solar panels [91,130]. Generated wastes should be chemically treated before dump- The proper collection of scrap panels, safe recycling and reduced ing into the sea, in order to protect the aquatic lives in the sea. emission procedure should be adopted. The proper guidelines for On-call systems should be developed for collection of dead- their handling have been discussed elsewhere [23,91,131–134]. solar-panels from houses for their safe disposal. Non-profit organization has come up in the market for the safe To minimize the cost of recycling, such modules should be disposal and recycling of PV modules. PV Cycle, along with the non- developed, which are easy to disassemble and detach the mate- profit association is working throughout Europe by targeting the rials from the glass. recycling rates of 80% and 85% by 2015 and 2020 respectively [135]. Water based eco-friendly solvent should be developed for and the leading solar panel manufacturer has started the cleaning dust and dirt from the solar panels. recycling of solar panels and continuously looking the ways of optimizing its recycling program. Approximately 90% of the module weight is recovered. Estimated recovery of semiconductor materials (Te and Cd) is 95%, which is quite good sign from SHE point of view, 6. Conclusion otherwise additional disposal cost will be required for proper disposalofgeneratedhardusedwastes[17,133,136,137]. The poten- This paper has summarized the Safety, Health and Environ- tial non-air impact of conventional and renewable energy power mental (SHE) impact of solar energy system on local inhabitants. sources have been summarized in Table A1. The production of solar energy systems in the world has increased majorly due to enormous amount of untapped solar potential, eco-friendly characteristics and to overcome possible energy fuel 5. Recommendations for a clean solar industry shortage in near future. Solar energy provides tremendous envir- onmental benefits when compared to the conventional energy Solar energy provides tremendous environmental benefits when sources. However solar systems also generate GHG emission compared to the conventional energy sources. In addition to preserve particularly in production stages and the waste of solar industry comes under e-garbage and must be handled carefully. Innovative production technologies in improving the PV modules module efficiency, increased lifetime, less silicon mass per module, lower use of electricity for the production process and proper recycling would help to lower the environmental impacts.

Acknowledgment

Authors would like to acknowledge the University of Malaya for funding the project under the project no. UM.K/636/1/HIR (MOHE)/ENG46.

Appendix A

Fig. 12. Existing concentrated solar power plants (CSP) [90]. See Table A1. 1202 M.M. Aman et al. / Renewable and Sustainable Energy Reviews 41 (2015) 1190–1204

Table A1 Potential non-air environmental impacts of several conventional power sources [138].

Power source Land use Water consumption Water quality/discharge Solid waste and ground Bio-diversity contamination

Coal High High Moderate to high High to low High Natural gas Moderate Low Zero to high (depends on Low Low the extraction method) Nuclear Moderate High High High Moderate to high Hydro with storage High Moderate Moderate Moderate Moderate Run of river hydro Low Low Zero Zero Low Solar PV and thermal electric High to low (depend on location Zero to low High to low Zero Zero where PV modules are mounted) Wind Moderate Zero Zero Low Low Geothermal Low Zero Low Zero Low Marine wave and tidal Low Zero Zero Zero Low Biomass High to low Moderate Moderate Low High

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